To facilitate the reduction to practice of this invention, applicants required a binder or food grade gum system capable of binding the high cellulose level in this product. The difficulty is related to the fact that the powdered cellulose is inert and does not function in any way as a binder of its own. Applicants found, during the course of their experimentation, that the normal gums utilized to bind this type of product (such as food grade starches, locust bean gum, wheat gluten and similar products) was ineffective in binding the high level of cellulose present in their product.
The specific product found to be satisfactory for this application is Methocel A4M Methylcellulose manufactured by Dow Chemical Company of Midland, Michigan. This product is manufactured by reacting cellulose with methylchloride in the presence of caustic soda, thereby producing cellulose ether. This product is currently utilized in the food industry as thickeners and emulsifiers in sauces such as salad dressings, barbecue sauces and various types of puddings. The product is also used in jams and jellies for preventing syneresis and, to some extent, in canned pet foods for providing emulsion stability and thickening gravy, but never as a cellulose binder. In current food uses for Methocel A4M Methylcellulose, the products are utilized in an aqueous system but not as a binder for a final dried product as in applicants' product.
Applicants believe that the gum discussed in the previous paragraph is beneficial for their application because it is different in at least one important respect from the majority of food grade gums and binders. This difference is that methocel, when heated, will thermally gel at a specific temperature. For Methocel A4M, this temperature is 50.degree.-55.degree. C. This inverse solubility, compared to that of other natural and synthetic gums, is the apparent reason that the material will bind the inert cellulose fibers. In their process, applicants create a gel system of the formulation during the heating and dehydration step. As the water is removed from the dog treat, the gel contracts slightly but maintains a matrix sufficient to bind the inert cellulose fibers.
The gelation can be explained by postulating that, during the dissolution process, the long thread-like polymer molecules are jacketed with layers of water molecules to increase the product bulk. These water molecules act as a lubricant, enabling the long cellulose ether chains to slide easily over one another and imparting to the solution the property of a smooth-pouring, viscous liquid. As the temperature increases, the viscosity initially decreases, the energy of these relatively loosely bound molecules increases and the outer layers of water molecules break away. When enough of the attached water molecules are driven away from the cellulose ether chains, the lubricating action is lost, the chains lock and the solution gels. A detailed description of the specific gum and the theory behind its binding nature is provided in the article entitled "Methocel Product Information" published by the Designed Products Department of the Dow Chemical Company of Midland, Michigan, in February, 1975.